No abstract

Bird-building collisions are the largest source of avian collision mortality in North America. Despite a growing literature on bird-building collisions, little research has been conducted in downtown areas of major cities, and no studies have included stadiums, which can be extremely large, often have extensive glass surfaces and lighting, and therefore may cause many bird collisions. Further, few studies have assessed the role of nighttime lighting in increasing collisions, despite the often-cited importance of this factor, or considered collision correlates for different seasons and bird species. We conducted bird collision monitoring over four migration seasons at 21 buildings, including a large multi-use stadium, in downtown Minneapolis, Minnesota, USA. We used a rigorous survey methodology to quantify among-building variation in collisions and assess how building features (e.g., glass area, lighting, vegetation) influence total collision fatalities, fatalities for separate seasons and species, and numbers of species colliding. Four buildings, including the stadium, caused a high proportion of all collisions and drove positive effects of glass area and amount of surrounding vegetation on most collision variables. Excluding these buildings from analyses resulted in slightly different collision predictors, suggesting that factors leading some buildings to cause high numbers of collisions are not the exact same factors causing variation among more typical buildings. We also found variation in collision correlates between spring and fall migration and among bird species, that factors influencing collision fatalities also influence numbers of species colliding, and that the proportion, and potentially area, of glass lighted at night are associated with collisions. Thus, reducing bird collisions at large buildings, including stadiums, should be achievable by reducing glass area (or treating existing glass), reducing light emission at night, and prioritizing mitigation efforts for glass surfaces near vegetated areas and/or avoiding use of vegetation near glass.

Bird collisions with buildings are the second largest anthropogenic source of direct mortality for birds (365–988 million birds killed annually in the United States). Recent research suggests that this mortality occurs disproportionately across species. However, previous work had relied on regional and annual measures of relative species abundance. Our research identifies which species experience higher or lower collision rates than expected from local abundances using two sets of citizen science data: Minnesota Project BirdSafe and the Mississippi River Twin Cities Important Bird Area Landbird Monitoring Program. Our analysis used a measure of relative species abundance that spatially overlaps the area monitored for building collisions and was measured weekly, allowing for a temporally and spatially more specific analysis than most previous analyses. Abundance and collision data were used to model phylogenetic and behavioral traits associated with increased collision risk. Behavioral traits included diurnal/nocturnal migration timing, length of migration, and foraging strategies. Our analysis shows that birds that predominately migrate during the day have a decreased risk of building collisions despite peak collision numbers occurring during early morning; this result suggests that more nuanced behavioral or physiological differences between diurnal and nocturnal migrants could contribute to bird-building collision risk. Additionally, for many species, local abundance is the predominant determining factor for collision risk. However, for ~20% of species studied, the family, genus, and/or species of a bird may affect the collision risk.

Weather appears to influence collisions of migratory birds with human‐built structures including buildings, but formal analyses are lacking. In 2018, as part of a two‐year study at 21 buildings in Minneapolis, Minnesota, USA, we observed a large number of American woodcock Scolopax minor collisions during two early spring snowstorms. We describe these events, analyze associations between weather and woodcock collisions during spring 2018, and compare observations to past studies across the woodcock's range. Most spring 2018 woodcock collisions (11 of 15; 73.3%) occurred in association with the two snowstorms. Analyses indicated collisions were positively associated with maximum and average wind speeds the night before collision surveys, and most collisions occurred with north winds. Collisions also increased with lower cloud base height two nights before surveys. These results support that woodcock collisions were greatly influenced by inclement weather, specifically the coincidence of strong north wind and low clouds. Comparing results to past studies illustrates that building collisions could be a major range‐wide source of woodcock mortality, especially in spring migration when mortality is likely additive. Although more research is needed to understand range‐wide, population‐level effects of woodcock collisions, management to reduce building collisions during migration may benefit woodcock populations. Additional research is needed to clarify effects of weather on bird collisions because management efforts could be refined if collisions of woodcocks and other bird species were forecastable like the weather.